Search for the K_{L}→π^{0}νν[over ¯] Decay at the J-PARC KOTO Experiment

Area of Science:

• Particle Physics
• High Energy Physics
• Rare Decay Searches

Background:

• The K_{L}→π^{0}νν decay is a rare process predicted by the Standard Model.
• Previous searches by the KOTO experiment have constrained its branching fraction.
• Understanding this decay provides insights into fundamental particle interactions.

Purpose of the Study:

• To search for the K_{L}→π^{0}νν decay using 2021 data from the J-PARC KOTO experiment.
• To set a new upper limit on the branching fraction for this rare decay.
• To search for the K_{L}→π^{0}X^{0} decay, where X^{0} is an invisible boson.

Main Methods:

• Utilized data collected in 2021 at the J-PARC KOTO experiment.
• Employed newly installed counters and an improved analysis method to suppress background.
• Calculated single event sensitivity and set upper limits at 90% confidence level.

Main Results:

• The expected background was significantly suppressed to 0.252±0.055_{stat}−0.067_{syst}^{+0.052}.
• No events were observed in the signal region for K_{L}→π^{0}νν.
• An upper limit on the branching fraction for K_{L}→π^{0}νν was set at 2.2×10^{-9}.
• An upper limit for K_{L}→π^{0}X^{0} was set at 1.6×10^{-9} for X^{0} with a mass of 135 MeV/c².

Conclusions:

• The search for K_{L}→π^{0}νν yielded no signal, resulting in an improved upper limit.
• The improved limit on the branching fraction for K_{L}→π^{0}νν enhances constraints on new physics.
• The search also provided constraints on the branching fraction of K_{L}→π^{0}X^{0} for invisible bosons.